In particular applications, fluid control valves having a high flow control range may be required. For example, a fluid control valve may be required where the pressure drop is large at low flow condition, but small at high flow condition. Traditional fluid control valves cannot meet these requirements, due to the large port size of larger fluid control valves.
One possible way to address these particular application is to use a large fluid control valve with a characterized cage. The cage in these fluid control valves are characterized to be multistage at low travel to resist the high pressure drop at low flow. Because of this, the fluid control valve has to be larger than a typical fluid control valve to provide the large flow control capacity. However, a larger fluid control valve usually has a large port size, so the control valve cannot control low or very low flow.
Another way to address these applications is to use two separated valves. By using two valves, a small valve can be used to control the low flow with high pressure drop and a large valve can be used to control the large flow control with low pressure drop. However, the use of two separated valves increases the cost and space requirements required for a particular installation.